[BI-2911] Remove rest of CRUD operations for ObservationDAO

[jloux-brapi]

Description

Story: BI-2911

• References to cache.post() were removed and replaced with brapiDAOUtil.post()
• References to cache.postThese() were removed and replaced with brapiDAOUtil.put()
• References to repopulate the observation cache were removed
• Extension of parent CachedDAO class removed

Dependencies

Testing

Checklist:

• I have performed a self-review of my own code
• I have tested my code and ensured it meets the acceptance criteria of the story
• I have create/modified unit and/or integration tests to cover this change or tests are not applicable
• I have commented my code, particularly in hard-to-understand areas
• I have either updated the source of truth or arranged for update with product owner if needed https://breedinginsight.atlassian.net/wiki/spaces/BI/pages/1559953409/Source+of+Truth